Migration of hydrogen through thin films of ZrO2 on Zr–Nb alloy

Abstract

The barrier properties of ZrO2 to inward migration of deuterium have been investigated with a view to understanding the hydriding mechanisms of a Zr-2.5% Nb alloy used in CANDU nuclear reactors fuel channels. Thin film oxide specimens, grown in steam to ∼1 μm thickness, have been heated to 350 °C and exposed to deuterium gas at pressures ranging from 6×10−3 Pa to 101 kPa (1 atm) and times from 10 to 810 min. Some irreversible uptake can be measured for all exposures using secondary ion mass spectrometry. At low exposures, the shape of the deuterium concentration profile is can be fitted to a Fickian relationship. During longer exposures, the rate of deuterium ingress is sharply curtailed, presumably due to passivated outer oxide surface. Reactions between D2O vapor and the thin film oxide in the 10−3 Pa pressure region and above show a sharply higher uptake of deuterium than in the equivalent pressure of D2 gas. This is ascribed to a more efficient decomposition of D2O on the ZrO2 surface compared to D2.

Tracer Film Growth Study of Hydrogen and Oxygen from the Corrosion of Magnesium in Water

“…2a, 2b). The 16 O signals in the as-polished surfaces decreased to the ∼10 2 to 10 3 c/s range on sputtering (Fig. 2c).…”

“…2c). The relatively high residual signal of 16 O likely reflects an inherent small impurity level of oxygen dissolved in the Mg (primarily as 16 O), as well as possible contributions from preferred instrument fractionation of the lighter 16 O vs 18 O. (The reason for the higher residual level of 16 O signal in the as-polished E717 sample relative to AZ31B and UHP Mg in Fig.…”

“…The data presented was limited to the total H signal (H + D) only (no distinction of isotopes) for the 4 h 18 O water + 20 h D 2 O exposure sequence and the as-polished controls. No separate data for H, D, 18 O, 16 O, or total O were reported in that work.…”

“…Ions were detected with a Balzers SEV 1217 electron multiplier coupled with an ion-counting system using an overall deadtime of 37 ns. Two isotopes of oxygen, 16 O and 18 O, and hydrogen, H and D were detected by switching the magnetic field.…”

“…[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Such insights have proven particularly useful for understanding the influence of various alloying additions on film growth, and provide a basis for improved alloy design. For example, tracer studies of Al 2 O 3 -forming alloys with and without rare earth element dopants revealed beneficial effects related to more protective, oxygen inward growth mechanisms [e.g.…”